Electric booster for vehicle

ABSTRACT

An electric booster for a vehicle includes a housing having a cylinder structure capable of supporting a hydraulic pressure formed therein; a screw bolt installed in the housing; a screw nut screwed to the screw bolt; a gear unit configured to transfer a rotational force of a motor to the screw nut; a rotation preventing unit coupled with the screw bolt, and configured to prevent rotation of the screw bolt by being brought into contact with the housing; and a piston moved by being pressed by the screw bolt, and configured to form a hydraulic pressure in the housing.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from and the benefit of Korean PatentApplication No. 10-2019-0045334, filed on Apr. 18, 2019, which is herebyincorporated by reference for all purposes as if set forth herein.

BACKGROUND Field

Exemplary embodiments of the present disclosure relate to an electricbooster for a vehicle, and more particularly, to an electric booster fora vehicle for increasing brake performance using electric power.

Discussion of the Background

In general, a brake device of a vehicle generates a frictional force bypushing a brake pad to decelerate a running vehicle or maintain a parkedstate. In this regard, since a driver's power is limited, brakeperformance is increased through boosting a force by a booster. While abooster using vacuum is employed in the related art, an electric boosterusing a motor is recently employed. The electric booster requires astructure capable of supporting forces acting in an axial direction anda radial direction when a brake is operated, and a rotation preventingstructure capable of preventing the rotation of a screw when a torque ofthe motor is transferred to the screw through gears to convert therotation of the motor into the linear movement of the screw.

In the related art, in order to realize the structure for supportingforces in an axial direction and a radial direction and the structurefor preventing the rotation of the screw, a structure in which aplurality of guide pins are disposed in parallel around the screw isemployed. Such guide pins mainly support a load generated by a hydraulicpressure in the electric booster, and guide a guide rod which isconnected with the screw, along a straight path.

However, in order to guide the guide rod along the guide pins, hollowspaces for securing a movement range of the guide rod are needed aroundthe guide pins. Therefore, the size of the electric booster increases,which is disadvantageous in terms of layout in disposing other parts ofthe vehicle. Further, the hollow spaces defined around the guide pinsserve as ringing spaces of the noise generated by the operation of thegears, which is disadvantageous in terms of noise.

Therefore, it is demanded in the art to cope with these problems.

A background art of the present disclosure is disclosed in Korean PatentLaid-open Publication No. 2014-0099270 (published on Aug. 11, 2014 andentitled ‘Electric Brake Booster’).

SUMMARY

Various embodiments are directed to an electric booster for a vehiclecapable of realizing miniaturization and noise reduction.

In an embodiment, an electric booster for a vehicle may include: ahousing having a cylinder structure capable of supporting a hydraulicpressure formed therein; a screw bolt installed in the housing; a screwnut screwed to the screw bolt; a gear unit configured to transfer arotational force of a motor to the screw nut; a rotation preventing unitcoupled with the screw bolt, and configured to prevent rotation of thescrew bolt by being brought into contact with the housing; and a pistonmoved by being pressed by the screw bolt, and configured to form ahydraulic pressure in the housing.

The rotation preventing unit may include: a rotation preventing diskpart coupled to the screw bolt; and one or more disk guide parts coupledto the housing, and configured to guide movement of the rotationpreventing disk part along a straight path.

The rotation preventing disk part may include: a disk portion disposedaround the screw bolt; one or more guide engagement portions formed toproject, on a circumferential outer surface of the disk portion, andinserted into the disk guide part; and a bolt coupling portion connectedwith the disk portion, and coupled to the screw bolt.

The bolt coupling portion may include: an extending portion connectedwith the disk portion; an assembly projection portion formed at an endof the extending portion, and brought into contact with an end of thescrew bolt; one or more assembly hole portions formed on the extendingportion to pass through the extending portion; and one or more lockingmembers locked to the screw bolt by passing through the assembly holeportion.

The assembly hole portion may include: an engagement receiving portionformed to be recessed, on an outer surface of the extending portion, ahead portion of the locking member being received in the engagementreceiving portion; and a through-hole portion formed to communicate withthe engagement receiving portion, a body portion of the locking memberpassing through the through-hole portion.

The rotation preventing disk part may further include: a spring assemblyportion formed on the disk portion to project toward the piston, andconfigured to prevent fluctuation of a spring which is disposed aroundthe piston.

The spring assembly portion may include: a spring assembly projectionportion formed to project, on the disk portion, extending concentricallywith the screw bolt, and an end of the spring being assembled; and anopening formed to be open, on the spring assembly projection portion, toallow the locking member of the bolt coupling portion to passtherethrough.

The disk guide part may include: a guide installation portion formed tobe recessed, on an inner surface of the housing, and extending along amovement path of the screw bolt; and a guide rail portion coupled to theguide installation portion, and configured to guide the rotationpreventing disk part along the straight path.

The guide rail portion may include: a rail body portion brought intocontact with an inner surface of the guide installation portion; and aguide groove formed to be recessed, on the rail body portion, configuredto receive the rotation preventing disk part, and extending along themovement path of the screw bolt.

The rail body portion may include: a first rail body portion broughtinto contact with the inner surface of the guide installation portion ina radial direction; and a second rail body portion formed at an end ofthe first rail body portion, and brought into contact with the innersurface of the guide installation portion in a moving direction of thescrew bolt.

The housing may include: a first housing unit having the piston and apart of the gear unit disposed therein; and a second housing unitconnected with the first housing unit, and having the screw nut and theother part of the gear unit disposed therein.

The first housing unit may include: a cylinder part formed with a pistonreceiving part in which the piston is received, and having a hydraulicpressure formed therein by movement of the piston; a motor connectingpart formed integrally with the cylinder part, and formed with a motorreceiving part in which an output shaft of the motor is received; and afirst gear box part formed between the cylinder part and the motorconnecting part to communicate with the cylinder part and the motorconnecting part, and formed with a first gear receiving part in which afirst gear of the gear unit connected with the output shaft and aportion of a second gear meshed with the first gear are received.

The first housing unit may further include: a first partitioning wallpart configured to partition the cylinder part and the motor connectingpart, and having one side which faces the piston receiving part and theother side which faces the motor receiving part.

The first housing unit may further include: a second partitioning wallpart configured to partition the motor connecting part and the firstgear box part, and having one side which faces the motor receiving partand the other side which faces the first gear receiving part.

The second partitioning wall part may include: a partitioning wall bodyportion configured to partition the motor connecting part and the firstgear box part; a bearing installation portion formed on the partitioningwall body portion to pass through the partitioning wall body portion,and having installed therein a bearing which rotatably supports theoutput shaft; and a first gear shaft support portion formed to berecessed, on the partitioning wall body portion, and configured torotatably support the second gear.

The second housing unit may include: a second gear box part formed witha second gear receiving part in which the other portion of the secondgear is received, and configured to communicate with the first gearreceiving part; and a boosting body part formed integrally with thesecond gear box part, and configured to receive a third gear of the gearunit, which is coupled with the screw nut.

The second gear box part may include: a box body portion; a second gearshaft support portion formed to be recessed, on the box body portion,and configured to rotatably support the first gear; and a third gearshaft support portion formed to be recessed, on the box body portion,and configured to rotatably support the second gear.

The gear unit may include: the first gear coupled to an output shaft ofthe motor; the second gear meshed with the first gear, and configured toprimarily decelerate rotation of the first gear; and the third gearcoupled with the screw nut, meshed with the second gear, and configuredto secondarily decelerate rotation of the second gear.

The second gear may include: a second input gear meshed with the firstgear; and a second output gear having a smaller diameter than the secondinput gear, coaxially connected with the second input gear, and meshedwith the third gear.

In the electric booster for a vehicle according to the embodiments ofthe present disclosure, a housing is fabricated to have a stiffness,that is, a thickness and a material, capable of directly supportingloads generated in an axial direction and a radial direction due to ahydraulic pressure and other loads generated in an axial direction and acircumferential direction, including an elastic force of a spring and arotational force acting on a rotation preventing unit, and the rotationof a screw bolt is prevented using the rotation preventing unit. As aconsequence, the application of guide pins which couple a plurality ofhousings with one another and at the same time guide the movement of ascrew bolt along a straight path in the related art may be omitted.

Therefore, in the present disclosure, when compared to the related artin which hollow spaces should be formed around the guide pins in anumber corresponding to the number of the guide pins to guide thereciprocating movement of the screw bolt using the guide pins, the guidepins and coupling means thereof may be omitted, and a size may bereduced by a size corresponding to the guide pins and the hollow spacesformed around the guide pins. As a consequence, the miniaturization anda light weight of the electric booster may be realized, advantages maybe provided in terms of layout in disposing other parts of a vehicle,and a problem caused by ringing of gear noise due to the presence of thehollow spaces may be solved.

Also, in the present disclosure, the housing has a compact structureincluding only a first housing unit and a second housing unit. That isto say, the number of divisions is minimized to two, that is, the numberof division parts and coupling parts which may degrade stiffness, isminimized. As a consequence, it is possible to more stably support theloads acting in an axial direction and a radial direction as describedabove.

Further, in the present disclosure, the first housing unit has astructure in which a motor housing and a boosting body according to therelated art are integrated, that is, has a structure in which a cylinderpart, a motor connecting part, a first gear box part, a firstpartitioning wall part and a second partitioning wall part areintegrally formed. As a consequence, a cantilever structure of an outputshaft may be improved, four locking means having a structure of O-ringsand male screws, which is applied in the related art, may be omitted,and a precision machining process for forming four locking holes, fourtabs and O-ring seats may be eliminated, thereby realizing a reductionin a manufacturing cost due to a reduction in the number of parts andfurther improving the productivity.

In the present disclosure, the first housing unit has the structure inwhich the cylinder part, the motor connecting part, the first gear boxpart, the first partitioning wall part and the second partitioning wallpart are integrally formed. As a consequence, it is possible not only toprevent precision and productivity from deteriorating due to machiningtolerances, assembly tolerances and allowances of the motor housing andthe boosting body, but also to form, in one body, two shaft supportelements which support rotation shafts of a first gear and a secondgear. In other words, since a bearing installation portion and a firstgear shaft support portion may be formed on the second partitioning wallpart, position allowances of the first gear and the second gear may besignificantly reduced, and noise due to the vibration of gear meshingportions may be reduced.

Moreover, in the present disclosure, the cylinder part and the motorconnecting part share the first partitioning wall part and the motorconnecting part and the first gear box part share the secondpartitioning wall part. As a consequence, when compared to the relatedart in which connection surface portions are defined in the motorhousing and the boosting body, respectively, and the motor housing andthe boosting body are coupled with each other with the connectionsurface portions disposed to overlap with each other, a size and aweight of the housing may be significantly reduced. Accordingly, since asize of the housing is further reduced, the layout is easy and isapplicable to various kinds of vehicles.

In the present disclosure, the cylinder part and the motor connectingpart share the first partitioning wall part. As a consequence, whencompared to the related art, a distance between the first gear and athird gear may be shortened by a thickness of the motor housing and aclearance between the motor housing and the boosting body that arereduced or eliminated, and accordingly, a design range of gears may befurther extended.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view schematically illustrating a representationof an example of an electric booster for a vehicle in accordance with anembodiment of the present disclosure.

FIG. 2 is a cross-sectional view taken along the line A-A′ of FIG. 1 .

FIG. 3 is a cross-sectional view taken along the line B-B′ of FIG. 1 .

FIG. 4 is a cross-sectional view taken along the line C-C′ of FIG. 1 .

FIG. 5 is an exploded perspective view schematically illustrating arepresentation of an example of a main part of the electric booster fora vehicle in accordance with the embodiment of the present disclosure.

FIG. 6 is a perspective view schematically illustrating a representationof an example of a rotation preventing disk part of the electric boosterfor a vehicle in accordance with the embodiment of the presentdisclosure.

FIG. 7 is a representation of an example of a conceptual diagram toassist in the explanation of the disposition of a gear unit of theelectric booster for a vehicle in accordance with the embodiment of thepresent disclosure.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Hereinafter, an electric booster for a vehicle will be described belowwith reference to the accompanying drawings through various examples ofembodiments. It should be noted that the drawings are not to precisescale and may be exaggerated in thickness of lines or sizes ofcomponents for descriptive convenience and clarity only. Furthermore,the terms as used herein are defined by taking functions of theinvention into account and can be changed according to the custom orintention of users or operators. Therefore, definition of the termsshould be made according to the overall disclosures set forth herein.

FIG. 1 is a perspective view schematically illustrating a representationof an example of an electric booster for a vehicle in accordance with anembodiment of the present disclosure, and FIG. 2 is a cross-sectionalview taken along the line A-A′ of FIG. 1 .

Referring to FIGS. 1 and 2 , the electric booster for a vehicle 1 inaccordance with the embodiment of the present disclosure includes ahousing 10, a screw bolt 20, a screw nut 30, a gear unit 40, a rotationpreventing unit 50, and a piston 60.

The housing 10 forms a space in which the screw bolt 20, the screw nut30, the gear unit 40, the rotation preventing unit 50 and the piston 60may be received, and at the same time, has a rigid structure capable ofsupporting a hydraulic pressure formed therein by the piston 60, anelastic force of a spring 70, a rotational force acting on the screwbolt 20, and so forth.

The screw bolt 20 is installed inside the housing 10, and the screw nut30 is screwed to the outer surface of the screw bolt 20. The gear unit40 transfers a rotational force of a motor 80 to the screw nut 30. Therotation preventing unit 50 is coupled with the screw bolt 20, and isbrought into contact with the housing 10 to prevent the rotation of thescrew bolt 20.

When the motor 80 is driven, the rotational force of the motor 80 isincreased while passing through the gear unit 40, and is transferred tothe screw nut 30. As the screw nut 30 is rotated in place, the screwbolt 20 is linearly moved toward one end or the other end of the housing10 when viewed from the screw nut 30. By this function, the rotationalmotion of the motor 80 is converted into the linear motion of the screwbolt 20. The piston 60 is pressed by the screw bolt 20 to be movedtoward the one end or the other end of the housing 10, and forms ahydraulic pressure inside the housing 10.

The present disclosure relates to an electric booster for a vehicle 1,and is based on the assumption that a driver's power and a force of theelectric booster for a vehicle 1 by the motor 80 are combined to realizethe function of an electric brake which generates a hydraulic pressurefor stopping a vehicle. In the following description of the presentdisclosure, for the sake of convenience in explanation, detaileddescriptions for structures, shapes and functions of components whichare not directly related with the subject matters of the presentdisclosure, such as a pedal rod 91, a reaction disk 92, a bearing member(drawing symbol not marked) and other components of an electric boosterfor a vehicle, will be omitted.

As such, the components of the electric booster for a vehicle which arenot disclosed in the description of the present disclosure are notlimited to specific structures and shapes, and may be applied togetherwith the present disclosure as various embodiments including well-knowntechniques in the technical field of the present disclosure. Inaddition, in the following description of the present disclosure, forthe sake of convenience in explanation, based on the extending directionof the screw bolt 20, a direction that is the same as or parallel to theextending direction of the screw bolt 20 is defined as an axialdirection, a direction that is perpendicular to the extending directionof the screw bolt 20 is defined as a radial direction, and a directionthat extends along the circumference of the screw bolt 20 is defined asa circumferential direction.

FIG. 3 is a cross-sectional view taken along the line B-B′ of FIG. 1 ,and FIG. 4 is a cross-sectional view taken along the line C-C′ of FIG. 1.

Referring to FIGS. 2 to 4 , the rotation preventing unit 50 inaccordance with the embodiment of the present disclosure includes arotation preventing disk part 51 and disk guide parts 56.

The rotation preventing disk part 51 is coupled and fixed to the screwbolt 20, and is moved by the same displacement together with the screwbolt 20. The disk guide parts 56 are coupled and fixed to the housing10, and guide the movement of the rotation preventing disk part 51 alonga straight path. The rotation of the rotation preventing disk part 51about the screw bolt 20 is prevented by the disk guide parts 56, and therotation preventing disk part 51 is slidingly moved only along thestraight path in the extending direction of the disk guide parts 56.

FIG. 5 is an exploded perspective view schematically illustrating arepresentation of an example of a main part of the electric booster fora vehicle in accordance with the embodiment of the present disclosure,and FIG. 6 is a perspective view schematically illustrating arepresentation of an example of the rotation preventing disk part of theelectric booster for a vehicle in accordance with the embodiment of thepresent disclosure.

Referring to FIGS. 2, 5 and 6 , the rotation preventing disk part 51 inaccordance with the embodiment of the present disclosure includes a diskportion 52, guide engagement portions 53, a bolt coupling portion 54,and a spring assembly portion 55.

The disk portion 52 has a circular shape corresponding to an inner spaceof the housing 10, and is disposed around the screw bolt 20. The guideengagement portions 53 are formed on a circumferential outer surface ofthe disk portion 52 to project in the radial direction, and are insertedand engaged into the disk guide parts 56. A plurality of guideengagement portions 53 are disposed with predetermined intervals.

Due to this fact, a rotational force transferred from the screw bolt 20to the disk portion 52 may be distributedly transferred to the pluralityof disk guide parts 56, and the rotation of the disk portion 52 may bemore stably prevented by the disk guide parts 56. While the presentembodiment of the disclosure illustrates a structure in which two guideengagement portions 53 are disposed on the circumferential outer surfaceof the disk portion 52 to be opposite to each other, it is to be notedthat at least three guide engagement portions may be disposed withpredetermined intervals.

The bolt coupling portion 54 assembles the disk portion 52 to an end ofthe screw bolt 20, and thereby, couples and fixes the disk portion 52and the screw bolt 20 to be moved with the same displacement. Referringto FIGS. 5 and 6 , the bolt coupling portion 54 in accordance with theembodiment of the present disclosure includes an extending portion 541,an assembly projection portion 542, an assembly hole portion 543, and alocking member 546.

The extending portion 541 has a cylindrical shape which extends in adirection parallel to the screw bolt 20, and is connected with the diskportion 52. The inner diameter portion of the extending portion 541 hasa diameter corresponding to the outer diameter portion of the screw bolt20. The assembly projection portion 542 is formed to project radiallyinward at an end of the extending portion 541.

When viewed in its entirety, the assembly projection portion 542 has adisk shape which has an inner diameter portion 542 a. The inner diameterportion 542 a of the assembly projection portion 542 has a diametersmaller than the outer diameter portion of the screw bolt 20 to bebrought into contact with the end of the screw bolt 20 in the axialdirection. The inner diameter portion of the assembly projection portion542 has the diameter through which the pedal rod 91 may pass, that is,the diameter that does not interfere with the movement of the pedal rod91.

The assembly hole portion 543 is formed to pass through the extendingportion 541 in the radial direction. The locking member 546 is locked tothe screw bolt 20 by passing through the assembly hole portion 543. Alocking groove portion 21 into which the end of the locking member 546may be inserted and locked may be formed in the end of the screw bolt20.

A bolt member or the like may be applied as the locking member 546, andthe locking groove portion 21 may have a structure of a female thread.The locking member 546 has a structure which includes a head portion 547and a body portion 548. The head portion 547 has an extended widthcompared to the body portion 548, and the body portion 548 is insertedinto the locking groove portion 21 by passing through the assembly holeportion 543. Referring to FIGS. 5 and 6 , the assembly hole portion 543in accordance with the embodiment of the present disclosure includes anengagement receiving portion 544 and a through-hole portion 545.

The engagement receiving portion 544 is formed to be recessed, in ashape corresponding to the head portion 547, from an outer surface ofthe extending portion 541. The through-hole portion 545 is formed on aninner surface of the extending portion 541 to extend in the radialdirection, and communicates with the engagement receiving portion 544.In a state in which the locking member 546 is coupled to the assemblyhole portion 543, the head portion 547 of the locking member 546 isreceived in the engagement receiving portion 544, and the body portion548 of the locking member 546 is inserted and locked into the lockinggroove portion 21 by passing through the through-hole portion 545. Therotation preventing disk part 51 is coupled and fixed to the screw bolt20 by the assembly structure described above.

The spring 70 for preventing the fluctuation of the rotation preventingdisk part 51 is interposed between the housing 10 and the disk portion52. The spring 70 has a structure of a coil spring, and is installedaround the piston 60 to be elastically deformable in the axialdirection. The spring assembly portion 55 as a device portion forpreventing the fluctuation and distortion of the spring 70 is formed onthe disk portion 52 to project toward the piston 60. Referring to FIG. 6, the spring assembly portion 55 in accordance with the embodiment ofthe present disclosure includes a spring assembly projection portion 551and an opening 553.

The spring assembly projection portion 551 as a device portion forforming an engagement projection preventing the fluctuation of an end ofthe spring 70 is formed on the disk portion 52 to project toward thespring 70 and the piston 60. The spring assembly projection portion 551extends concentrically with the screw bolt 20 while having a circularshape.

The end of the spring 70 which has the structure of a coil spring isfitted around the outer diameter portion of the spring assemblyprojection portion 551 or is fitted between the spring assemblyprojection portion 551 and the extending portion 541 to be constrainedin place on the disk portion 52, and may apply an elastic pressing forceevenly over the disk portion 52 having a circular shape.

The opening 553 is formed to be open at a position of the springassembly projection portion 551 corresponding to the assembly holeportion 543 so as to allow the spring assembly projection portion 551not to interfere with the assembly of the locking member 546. Thelocking member 546 may be inserted and locked into the assembly holeportion 543 positioned inside the spring assembly projection portion551, by passing through the opening 553.

Referring to FIGS. 2, 4 and 5 , each disk guide part 56 in accordancewith the embodiment of the present disclosure includes a guideinstallation portion 57 and a guide rail portion 58.

The guide installation portion 57 is formed to be recessed in the radialdirection, at a position on an inner surface of the housing 10corresponding to the guide engagement portion 53. The guide installationportion 57 is formed to extend along a movement path of the screw bolt20. The guide rail portion 58 as a device portion guiding the rotationpreventing disk part 51 along a straight path is coupled to the guideinstallation portion 57. Referring to FIG. 5 , the guide rail portion 58in accordance with the embodiment of the present disclosure includes arail body portion 581 and a guide groove 584.

The rail body portion 581 as a device portion forming a basic frame ofthe guide rail portion 58 is inserted into the guide installationportion 57 which has a recessed shape, and thereby, is coupled to aninner surface of the guide installation portion 57. Referring to FIG. 5, the rail body portion 581 in accordance with the embodiment of thepresent disclosure includes a first rail body portion 582 and a secondrail body portion 583.

The first rail body portion 582 as a device portion which is broughtinto contact with the inner surface of the guide installation portion 57in the radial direction is formed to extend in the axial direction ofthe screw bolt 20, and has a U-shaped cross-sectional shape whose oneend facing the rotation preventing disk part 51 is open. The second railbody portion 583 is formed to extend radially inward, at an end of thefirst rail body portion 582 facing the guide installation portion 57 inthe axial direction.

The guide installation portion 57 has an arc-shaped cross-sectionalshape corresponding to the inner surface of the housing 10 having acircular cross-sectional shape, with respect to the radial directionperpendicular to the axial direction of the screw bolt 20, and an outersurface of the first rail body portion 582 also has an arc-shapedcross-sectional shape corresponding thereto. An outer surface of thesecond rail body portion 583 has a shape which extends in the radialdirection, and is brought into surface contact with an inner surface ofthe guide installation portion 57 in the axial direction.

The rail body portion 581 may be stably coupled and fixed in a state inwhich the rail body portion 581 is brought into surface contact with theguide installation portion 57 in various directions including the radialdirection and the axial direction, as described above. The guide groove584 is formed between the first rail body portion 582 and the secondrail body portion 583, and the guide engagement portion 53 which ismoved along the guide groove 584 is prevented from directly coming intocontact or colliding with the guide installation portion 57 integrallyformed with the housing 10, by being brought into contact with thesecond rail body portion 583.

The guide groove 584 is formed to be recessed, on the rail body portion581, and is formed to extend along the movement path of the screw bolt20. In a state in which the guide engagement portion 53 is inserted intothe guide groove 584, the guide engagement portion 53 is engaged withthe first rail body portion 582 having the U-shaped cross-sectionalshape to be prevented from being rotated in the circumferentialdirection, and is moved only in the extending direction of the guidegroove 584 formed to extend along the first rail body portion 582, thatis, only in the axial direction of the screw bolt 20.

A hydraulic pressure is formed inside the housing 10 by the movement ofthe piston 60, and loads generated in the axial direction and the radialdirection due to such a hydraulic pressure are directly transferred tothe housing 10, without the medium of separate components, to be mainlysupported by the housing 10. Also, the housing 10 directly supportsother axial and circumferential loads including the elastic force of thespring 70, a rotational force acting on the rotation preventing unit 50,and so forth.

The housing 10 is fabricated to have a stiffness, that is, a thicknessand a material, capable of directly supporting such axial, radial, andcircumferential loads. Also, the housing 10 has a compact structureincluding only a first housing unit 11 and a second housing unit 17.That is to say, the number of divisions is minimized to two, that is,the number of division parts and coupling parts for coupling thedivision parts, which may degrade stiffness, is minimized. As aconsequence, it is possible to more stably support the loads acting inthe axial direction and the radial direction as described above.

Moreover, since the rotation of the screw bolt 20 may be stablyprevented using the rotation preventing unit 50, a rotational forcetransferred from the screw nut 30 to the screw bolt 20 may be clearlyconverted into a linear movement of the screw bolt 20. Further, only byadditionally forming a small space corresponding to a movement range ofthe guide engagement portion 53 in addition to forming a space capableof receiving the screw bolt 20, the screw nut 30 and the piston 60inside the housing 10, the above-described function may be realized.

In the related art, by coupling a plurality of housings 10 to oneanother and at the same time guiding the movement of the screw bolt 20along a straight path through using guide pins (not illustrated), theguide pins mainly support loads generated by a hydraulic pressure, andhollow spaces (not illustrated) need to be formed around the guide pinsin a number corresponding to the number of the guide pins to guide thereciprocating movement of the screw bolt 20.

According to the present disclosure, when compared to such a relatedart, a size may be reduced by a size corresponding to the guide pins andthe hollow spaces formed around the guide pins. As a consequence, theminiaturization and a light weight of an electric booster 1 may berealized, advantages may be provided in terms of layout in disposingother parts of a vehicle, and a problem caused by ringing of gear noisedue to the presence of the hollow spaces may be solved.

FIG. 7 is a representation of an example of a conceptual diagram toassist in the explanation of the disposition of the gear unit of theelectric booster for a vehicle in accordance with the embodiment of thepresent disclosure.

Referring to FIGS. 3 and 7 , the gear unit 40 in accordance with theembodiment of the present disclosure includes a first gear 41, a secondgear 42, and a third gear 45.

The first gear 41 is coupled to an output shaft 81 of the motor 80. Thesecond gear 42 meshes with the first gear 41. Referring to FIGS. 3 and 7, the second gear 42 in accordance with the embodiment of the presentdisclosure includes a second input gear 43 and a second output gear 44.The second input gear 43 has a larger diameter than the first gear 41,and meshes with the first gear 41. The second output gear 44 has asmaller diameter than the second input gear 43, is coaxially connectedwith the second input gear 43, and is rotated with the same angulardisplacement as the second input gear 43.

The third gear 45 has a larger diameter than the second output gear 44,is coupled and fixed to an outer surface of the screw nut 30, and mesheswith the second output gear 44. The rotation of the first gear 41 isprimarily decelerated while being transferred to the second input gear43, and the rotation of the second output gear 44 is secondarilydecelerated while being transferred to the third gear 45. Namely, arotational force of the first gear 41 is primarily increased while beingtransferred to the second input gear 43, is secondarily increased whilebeing transferred from the second output gear 44 to the third gear 45,and is then transferred to the screw nut 30.

Referring to FIGS. 1 and 3 , the housing 10 in accordance with theembodiment of the present disclosure includes the first housing unit 11and the second housing unit 17.

The first housing unit 11 receives the piston 60 and a part of the gearunit 40, more specifically, the piston 60, one ends of the screw bolt 20pressing the piston 60 and the screw nut 30, the rotation preventingunit 50, the reaction disk 92, the output shaft 81 of the motor 80, thefirst gear 41, and the second input gear 43.

The second housing unit 17 receives the other parts of the screw nut 30and the gear unit 40, more specifically, the pedal rod 91, the otherends of the screw bolt 20 and the screw nut 30, the second output gear44 and the third gear 45. The second housing unit 17 is fabricatedseparately from the first housing unit 11, and is locked and coupledwith the first housing unit 11 by locking means (not illustrated). In astate in which the ends of the first housing unit 11 and the secondhousing unit 17 are brought into contact with each other, onecommunicating space is formed inside the first housing unit 11 and thesecond housing unit 17.

Referring to FIGS. 1 and 3 , the first housing unit 11 in accordancewith the embodiment of the present disclosure includes a cylinder part12, a motor connecting part 13, a first gear box part 14, a firstpartitioning wall part 15, and a second partitioning wall part 16.

The cylinder part 12 has a cylinder shape in which the piston 60disposed therein may be moved along a straight path. Inside the cylinderpart 12, in addition to the piston 60, the one ends of the screw bolt 20pressing the piston 60 and the screw nut 30, the rotation preventingunit 50, and the reaction disk 92 are received. In the description ofthe present disclosure, an inner space of the cylinder part 12 isreferred to as a piston receiving part 12 a.

A hydraulic pressure is formed inside the cylinder part 12 by themovement of the piston 60, and the vehicle is braked using the hydraulicpressure formed inside the cylinder part 12 in this way. The motorconnecting part 13 has a cylindrical shape which may receive the outputshaft 81 of the motor 80, and is formed such that a portion of the motorconnecting part 13 to be coupled with the motor 80 is open. In thedescription of the present disclosure, an inner space of the motorconnecting part 13 is referred to as a motor receiving part 13 a.

The first gear box part 14 is formed between the cylinder part 12 andthe motor connecting part 13 to communicate with the cylinder part 12and the motor connecting part 13. The first gear 41 which is connectedwith the output shaft 81 and the second input gear 43 are received inthe first gear box part 14. In the description of the presentdisclosure, an inner space of the first gear box part 14 is referred toas a first gear receiving part 14 a.

The first partitioning wall part 15 as a device part forming apartitioning wall which partitions the cylinder part 12 and the motorconnecting part 13 is disposed between the cylinder part 12 and themotor connecting part 13. One side of the first partitioning wall part15 faces the piston receiving part 12 a, and the other side of the firstpartitioning wall part 15 faces the motor receiving part 13 a.

The second partitioning wall part 16 as a device part forming apartitioning wall which partitions the motor connecting part 13 and thefirst gear box part 14 is disposed between the motor connecting part 13and the first gear box part 14. One side of the second partitioning wallpart 16 faces the motor receiving part 13 a, and the other side of thesecond partitioning wall part 16 faces the first gear receiving part 14a. Referring to FIG. 3 , the second partitioning wall part 16 inaccordance with the embodiment of the present disclosure includes apartitioning wall body portion 161, a bearing installation portion 162,and a first gear shaft support portion 163.

The partitioning wall body portion 161 forms a partitioning wall whichpartitions the motor connecting part 13 and the first gear box part 14.The bearing installation portion 162 is formed on the partitioning wallbody portion 161 to pass through the partitioning wall body portion 161,and a bearing 82 which rotatably supports the output shaft 81 isinstalled in the bearing installation portion 162. The first gear shaftsupport portion 163 is formed to be recessed, on the partitioning wallbody portion 161, and rotatably supports a rotation shaft (drawingsymbol not marked) of the second gear 42.

Referring to FIG. 3 , the second housing unit 17 in accordance with theembodiment of the present disclosure includes a second gear box part 18and a boosting body part 19.

The second output gear 44 is received inside the second gear box part18. In the description of the present disclosure, an inner space of thesecond gear box part 18 is referred to as a second gear receiving part18 a. The second gear box part 18 adjoins the first gear box portion 14,and the second gear receiving part 18 a communicates with the first gearreceiving part 14 a. Referring to FIG. 3 , the second gear box part 18in accordance with the embodiment of the present disclosure includes abox body portion 181, a second gear shaft support portion 182, and athird gear shaft support portion 183.

The box body portion 181 has a shape which may receive the second outputgear 44. The second gear shaft support portion 182 is formed to berecessed, on the box body portion 181, and rotatably supports the firstgear 141, that is, an end of the output shaft 81 to which the first gear41 is coupled. The output shaft 81 passes through the bearinginstallation portion 162, and the end of the output shaft 81 is insertedinto the second gear shaft support portion 182.

The third gear shaft support portion 183 is formed to be recessed, onthe box body portion 181, and rotatably supports the second gear 42. Thethird gear shaft support portion 183 is formed to face the first gearshaft support portion 163. Both ends of the rotation shaft (drawingsymbol not marked) of the second gear 42 are supported by the first gearshaft support portion 163 and the third gear shaft support portion 183,respectively, and in this state, are rotated in place by a rotationalforce transferred to the second gear 42.

The boosting body part 19 is formed integrally with the second gear boxpart 18, and adjoins the cylinder part 12. Inside the boosting body part19, there are received the pedal rod 91, the other ends of the screwbolt 20 and the screw nut 30, and the third gear 45. In the descriptionof the present disclosure, an inner space of the boosting body part 19is referred to as a bolt nut receiving part 19 a. In a state in whichthe boosting body part 19 and the cylinder part 12 are brought intocontact with each other, the bolt nut receiving part 19 a forms onecommunicating cylindrical space together with the piston receiving part12 a. The screw bolt 20 is reciprocatingly moved toward the pistonreceiving part 12 a or the bolt nut receiving part 19 a in liaison withthe rotation of the screw nut 30.

In the related art, the output shaft 81 of the motor 80 is received in ahousing 10 which is commonly referred to as a ‘motor housing’ (notillustrated), the second input gear 43 is received in a separate housing10 which is commonly referred to as a ‘boosting body’ (not illustrated),and the motor housing and the boosting body are coupled to each otherusing separate coupling means. The boosting body has a structure inwhich a first boosting body (not illustrated) receiving the piston 60and a second boosting body (not illustrated) receiving the pedal rod 91are coupled to each other.

In the related art, since the output shaft 81 of the motor 80 has acantilever structure, it is vulnerable to sagging or vibration.Therefore, in general, the motor housing and the boosting body have astructure in which they are bolted at a plurality of placescorresponding to four places. Accordingly, when mutually coupling themotor housing and the boosting body, the number of precision machiningprocesses and the number of parts for assembly and sealing increase.More specifically, the number of precision machining processes and thenumber of parts increase in correspondence to precision machining offour holes (not illustrated), four tabs (not illustrated), O-rings (notillustrated) and O-ring seats (not illustrated).

Also, in the related art, the output shaft 81 is disposed in place wheremeshing with the gear unit 40 is implemented, through cumbersome andinvolved processes of matching the center of the output shaft 81 withthe second boosting body by coupling the O-rings installed on an outersurface of the motor housing to the first boosting body and of lockingmeans (not illustrated) each having a male screw structure to the tabsof the motor housing through holes of the boosting body.

Further, in the related art, the concentricity of the motor housing andthe boosting body may be degraded not only by a clearance that occurs ata connection between the motor housing and the boosting body, such asO-ring coupling parts (not illustrated), during such an assemblyprocess, but also by assembly tolerances of the locking means.

Moreover, in the related art, in order to form the plurality of tabsaround the output shaft 81 of the motor 80, a size of the motor housingneeds to be larger than a size capable of receiving the output shaft 81,and a size of the boosting body also needs to be increased to form theplurality of holes. As a consequence, an overall size and weight of adevice increase, and a lot of a material is consumed in the manufactureof the housing 10.

In addition, in the related art, the motor housing and the boosting bodycannot help but not only have respective thicknesses, but also beassembled with each other with clearances in consideration ofmanufacturing and assembly tolerances, allowances, and the likes.Accordingly, it was impossible to reduce a distance between the firstgear 41 coupled to the motor housing and the third gear 45 disposed inthe boosting body to be shorter than an interval corresponding to d1illustrated in FIG. 7 .

According to the present disclosure having the above-mentionedconfiguration, as the first housing unit 11 has a structure in which themotor housing and the boosting body of the related art are integrated,that is, a structure in which the cylinder part 12, the motor connectingpart 13, the first gear box part 14, the first partitioning wall part 15and the second partitioning wall part 16 are integrally formed, thehousing 10 has a compact structure including only the first housing unit11 and the second housing unit 17, that is, a structure in which thenumber of divisions is minimized to two.

Therefore, according to the present disclosure, the cantilever structureof the output shaft 81 is improved, and the O-rings and the four lockingmeans each having a male screw structure which are applied in therelated art may be omitted. Besides, since the precision machiningprocesses for forming the four locking holes, the four tabs and theO-ring seats may be eliminated, it is possible to realize cost reductiondue to a reduction in the number of parts and it is possible to furtherimprove the productivity.

Also, according to the present disclosure, the first housing unit 11 hasthe structure in which the cylinder part 12, the motor connecting part13, the first gear box part 14, the first partitioning wall part 15 andthe second partitioning wall part 16 are integrally formed. As aconsequence, it is possible not only to prevent precision andproductivity from deteriorating due to machining tolerances, assemblytolerances and allowances of the motor housing and the boosting body,but also to form, in one body, two shaft support elements which supportthe rotation shafts (drawing symbol not marked) of the first gear 41 andthe second gear 42. In other words, since the bearing installationportion 162 and the first gear shaft support portion 163 may be machinedon the second partitioning wall part 16, position allowances of thefirst gear 41 and the second gear 42 may be significantly reduced, andnoise due to the vibration of gear meshing portions may be reduced.

Further, according to the present disclosure, the cylinder part 12 andthe motor connecting part 13 share the first partitioning wall part 15,and the motor connecting part 13 and the first gear box part 14 sharethe second partitioning wall part 16. As a consequence, when compared tothe related art in which connection surface portions are defined in themotor housing and the boosting body, respectively, and the motor housingand the boosting body are coupled with each other with the connectionsurface portions disposed to overlap with each other, a size and aweight of the housing 10 may be significantly reduced. Accordingly,since a size of the housing 10 is further reduced, the layout is easyand is applicable to various kinds of vehicles.

Moreover, according to the present disclosure, the cylinder part 12 andthe motor connecting part 13 share the first partitioning wall part 15.As a consequence, when compared to the related art, a distance betweenthe first gear 41 and the third gear 45 may be shortened by a thicknessof the motor housing and a clearance between the motor housing and theboosting body that are reduced or eliminated, that is, by d2 illustratedin FIG. 7 . If necessary, a design range of gears may be furtherextended, such as by disposing the first gear 41 on a line L1 ordisposing the first gear 41 on a line L2.

Although preferred embodiments of the disclosure have been disclosed forillustrative purposes, those skilled in the art will appreciate thatvarious modifications, additions and substitutions are possible, withoutdeparting from the scope and spirit of the disclosure as defined in theaccompanying claims. Thus, the true technical scope of the disclosureshould be defined by the following claims.

What is claimed is:
 1. An electric booster for a vehicle, comprising: a housing having a cylinder structure capable of supporting a hydraulic pressure formed therein; a screw bolt installed in the housing; a screw nut screwed to the screw bolt; a gear unit configured to transfer a rotational force of a motor to the screw nut; a rotation preventing unit coupled with the screw bolt, and configured to prevent rotation of the screw bolt by being brought into contact with the housing; and a piston moved by being pressed by the screw bolt, and configured to form a hydraulic pressure in the housing, wherein the rotation preventing unit comprises: a rotation preventing disk part coupled to the screw bolt; and one or more disk guide parts coupled to the housing, and configured to guide movement of the rotation preventing disk part along a straight path, and wherein the rotation preventing disk part comprises: a disk portion disposed around the screw bolt; one or more guide engagement portions formed to project, on a circumferential outer surface of the disk portion, and inserted into the disk guide part; and a bolt coupling portion connected with the disk portion, and coupled to the screw bolt.
 2. The electric booster for a vehicle according to claim 1, wherein the bolt coupling portion comprises: an extending portion connected with the disk portion; an assembly projection portion formed at an end of the extending portion, and brought into contact with an end of the screw bolt; one or more assembly hole portions formed on the extending portion to pass through the extending portion; and one or more locking members locked to the screw bolt by passing through the assembly hole portion.
 3. The electric booster for a vehicle according to claim 2, wherein the assembly hole portion comprises: an engagement receiving portion formed to be recessed, on an outer surface of the extending portion, a head portion of the locking member being received in the engagement receiving portion; and a through-hole portion formed to communicate with the engagement receiving portion, a body portion of the locking member passing through the through-hole portion.
 4. The electric booster for a vehicle according to claim 1, wherein the rotation preventing disk part further comprises: a spring assembly portion formed on the disk portion to project toward the piston, and configured to prevent fluctuation of a spring which is disposed around the piston.
 5. The electric booster for a vehicle according to claim 4, wherein the spring assembly portion comprises: a spring assembly projection portion formed to project, on the disk portion, extending concentrically with the screw bolt, and an end of the spring being assembled; and an opening formed to be open, on the spring assembly projection portion, to allow the locking member of the bolt coupling portion to pass therethrough.
 6. An electric booster for a vehicle, comprising: a housing having a cylinder structure capable of supporting a hydraulic pressure formed therein; a screw bolt installed in the housing; a screw nut screwed to the screw bolt; a gear unit configured to transfer a rotational force of a motor to the screw nut; a rotation preventing unit coupled with the screw bolt, and configured to prevent rotation of the screw bolt by being brought into contact with the housing; and a piston moved by being pressed by the screw bolt, and configured to form a hydraulic pressure in the housing, wherein the rotation preventing unit comprises: a rotation preventing disk part coupled to the screw bolt; and one or more disk guide parts coupled to the housing, and configured to guide movement of the rotation preventing disk part along a straight path, and wherein the disk guide part comprises: a guide installation portion formed to be recessed, on an inner surface of the housing, and extending along a movement path of the screw bolt; and a guide rail portion disposed at the recessed guide installation portion, and configured to guide the rotation preventing disk part along the straight path.
 7. The electric booster for a vehicle according to claim 6, wherein the guide rail portion comprises: a rail body portion brought into contact with an inner surface of the guide installation portion; and a guide groove formed to be recessed, on the rail body portion, configured to receive the rotation preventing disk part, and extending along the movement path of the screw bolt.
 8. The electric booster for a vehicle according to claim 7, wherein the rail body portion comprises: a first rail body portion brought into contact with the inner surface of the guide installation portion in a radial direction; and a second rail body portion formed at an end of the first rail body portion, and brought into contact with the inner surface of the guide installation portion in a moving direction of the screw bolt.
 9. An electric booster for a vehicle, comprising: a housing having a cylinder structure capable of supporting a hydraulic pressure formed therein; a screw bolt installed in the housing; a screw nut screwed to the screw bolt; a gear unit configured to transfer a rotational force of a motor to the screw nut; a rotation preventing unit coupled with the screw bolt, and configured to prevent rotation of the screw bolt by being brought into contact with the housing; and a piston moved by being pressed by the screw bolt, and configured to form a hydraulic pressure in the housing, wherein the housing comprises: a first housing unit having the piston and a part of the gear unit disposed therein; and a second housing unit connected with the first housing unit, and having the screw nut and the other part of the gear unit disposed therein.
 10. The electric booster for a vehicle according to claim 9, wherein the first housing unit comprises: a cylinder part formed with a piston receiving part in which the piston is received, and having a hydraulic pressure formed therein by movement of the piston; a motor connecting part formed integrally with the cylinder part, and formed with a motor receiving part in which an output shaft of the motor is received; and a first gear box part formed between the cylinder part and the motor connecting part to communicate with the cylinder part and the motor connecting part, and formed with a first gear receiving part in which a first gear of the gear unit connected with the output shaft and a portion of a second gear meshed with the first gear are received.
 11. The electric booster for a vehicle according to claim 10, wherein the first housing unit further comprises: a first partitioning wall part configured to partition the cylinder part and the motor connecting part, and having one side which faces the piston receiving part and the other side which faces the motor receiving part.
 12. The electric booster for a vehicle according to claim 10, wherein the first housing unit further comprises: a second partitioning wall part configured to partition the motor connecting part and the first gear box part, and having one side which faces the motor receiving part and the other side which faces the first gear receiving part.
 13. The electric booster for a vehicle according to claim 12, wherein the second partitioning wall part comprises: a partitioning wall body portion configured to partition the motor connecting part and the first gear box part; a bearing installation portion formed on the partitioning wall body portion to pass through the partitioning wall body portion, and having installed therein a bearing which rotatably supports the output shaft; and a first gear shaft support portion formed to be recessed, on the partitioning wall body portion, and configured to rotatably support the second gear.
 14. The electric booster for a vehicle according to claim 10, wherein the second housing unit comprises: a second gear box part formed with a second gear receiving part in which the other portion of the second gear is received, and configured to communicate with the first gear receiving part; and a boosting body part formed integrally with the second gear box part, and configured to receive a third gear of the gear unit, which is coupled with the screw nut.
 15. The electric booster for a vehicle according to claim 14, wherein the second gear box part comprises: a box body portion; a second gear shaft support portion formed to be recessed, on the box body portion, and configured to rotatably support the first gear; and a third gear shaft support portion formed to be recessed, on the box body portion, and configured to rotatably support the second gear.
 16. An electric booster for a vehicle, comprising: a housing having a cylinder structure capable of supporting a hydraulic pressure formed therein; a screw bolt installed in the housing; a screw nut screwed to the screw bolt; a gear unit configured to transfer a rotational force of a motor to the screw nut; a rotation preventing unit coupled with the screw bolt, and configured to prevent rotation of the screw bolt by being brought into contact with the housing; and a piston moved by being pressed by the screw bolt, and configured to form a hydraulic pressure in the housing, wherein the gear unit comprises; the first gear coupled to an output shaft of the motor; the second gear meshed with the first gear, and configured to primarily decelerate rotation of the first gear; and the third gear coupled with the screw nut, meshed with the second gear, and configured to secondarily decelerate rotation of the second gear.
 17. The electric booster for a vehicle according to claim 16, wherein the second gear comprises: a second input gear meshed with the first gear; and a second output gear having a smaller diameter than the second input gear, coaxially connected with the second input gear, and meshed with the third gear. 